Materials such as group IV semiconductors (crystalline and amorphous types), compound semiconductors (group III-V, group II-VI, group I-III-VI, transition metal silicides, etc.), and organic semiconductors (coloring matters, polymers, etc.) have been in use in photoelectric transducers employed in solar batteries (cells) and the like. Among these device materials, the compound semiconductors are advantageous in that they have a high optical absorption coefficient and a bandgap (bandgap energy: Eg) suitable for yielding a favorable photoelectric conversion efficiency.
Various structures such as pn junction, pin junction, and heterojunction have been known as modes of junctions of layers constituting a photoelectric transducer. The pin junction, in which a major part of photoelectrons and positive holes occur in a layer having an internal electric field (depletion layer), can generate a greater current than does the pn junction, and thus can eliminate the process of moving a carrier by diffusing it into a pn boundary which is seen in the pn junction. Therefore, the pin junction has recently been in wide use in so-called amorphous solar batteries.
Attention has further been focused on iron silicide which shows a semiconductor characteristic among transition metal silicides as an i-layer (intrinsic semiconductor layer) of a photoelectric transducer having a pin junction. Iron silicide is constituted by iron and silicon which are elements exhibiting a low environmental load and a long resource life. Also, iron silicide is a material exhibiting a small lattice mismatch with silicon substrates which are typically in use in semiconductor apparatus, while being widely excellent in optical, electric, magnetic, and thermoelectric characteristics.
Iron silicide expressed by FexSiy in general exhibits a plurality of kinds of crystal phases mainly depending on its growth conditions and the composition ratio (x:y) between iron and silicon atoms. Of crystalline types of iron silicide, one having a semiconductor characteristic has been known to be β-FeSi2, whereas various techniques have been proposed as methods of forming the same. Among them, methods disclosed in Patent Documents 1 to 4, for example, can be adopted for β-FeSi2 employable in devices having a large area such as photoelectric transducers and methods of forming the same.
[Patent Document 1] Japanese Patent Application Laid-Open No. HEI 4-210463
[Patent Document 2] Japanese Patent Application Laid-Open No. HEI 7-166323
[Patent Document 3] Japanese Patent Application Laid-Open No. 2001-64099
[Patent Document 4] Japanese Patent Application Laid-Open No. 2002-47569